Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $84.39   9.768%   $92.6332   $92.63   $92.65   $92.60  
  Purchase #2 $128.60   5.720%   $135.9559   $135.96   $135.95   $136.00  
  Purchase #3 $114.35   11.690%   $127.7175   $127.72   $127.70   $127.70  
  Purchase #4 $201.95   12.765%   $227.7289   $227.73   $227.75   $227.70  
  Purchase #5 $23.65   11.182%   $26.2945   $26.29   $26.30   $26.30  
  Purchase #6 $198.98   8.290%   $215.4754   $215.48   $215.50   $215.50  
  Purchase #7 $50.58   12.478%   $56.8914   $56.89   $56.90   $56.90  
  7 purchase totals = $802.50       $882.6968   $882.70   $882.75   $882.70